PPT Slide

SIMPLE ARITHMETIC and IS

Predicates are only true or false.

We need functions to do arithmetic.

But if a function returns a value, can we assign that value to a variable?

Yes, using the “is” operator.

twice( Y , X ) : - Y is 2 * X .

|?- X is 4 / 2 .

X = 2

|?- X is 5 / 2 .

X = 2.5

|?- twice( 4 , 2 ) .

Yes

|?- twice( Z , 4 ) .

Z = 8

|?- twice( 4 , Z ) .

EXCEPTION

P.22

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